This application claims the priority of Japanese Patent Applications Nos. 8-263475 and 8-263476 filed on Sept. 12, 1996, Nos. 8-267925 and 8-267926 filed on Sept. 17, 1996, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic endoscope system, and particularly to the signal-processing for an endoscope system in which the all pixels of an image stored in an image pickup device by one exposure are read out to form an image of high quality.
2. Description of the Prior Art
In the electronic endoscope system, a device such as a CCD (Charge Coupled Device) is used as the image pickup device, and in the CCD, an image signal (video signal) is obtained by reading out the charges stored by an optoelectric transducer on a pixel basis. And, in the simultaneous electronic endoscope system, color filters are placed on the upper surface of the CCD for each pixel, thereby to obtain a color image.
In FIG. 17(A), the arrangement of the above color filters is shown, and on the image pickup surface of a CCD 1, Mg (magenta), G (green), Cy (cyan), and Ye (yellow), for instance, are arranged on a pixel basis as shown. Accordingly, by a light passing through these color filters, stored charges are obtained in the CCD 1.
FIG. 17(B) shows the reading by the conventional 2-line mixed reading method, in which the stored charges of the pixels in the upper and lower lines are mixed and read out. For instance, in the first exposure, odd field video signals such as a mixed signal of line 0 and line 1, a mixed signal of line 2 and line 3 . . . are read out, and in the second exposure, even field video signals such as a mixed signal of line 1 and line 2, a mixed signal of line 3 and line 4 . . . are read out. Accordingly, the mixed signals of two lines of the CCD 1 become the signal of one line of a field image.
In FIG. 18, the signal read operation in the above CCD 1 is shown, and as shown by the field O/E signal of (A) of the same figure, odd and even fields are obtained for each 1/60 sec (vertical synchronizing period). For this, in the above period of 1/60 sec, a signal storing is performed, for instance, by the storage (exposure) time t of an electronic shutter shown in (B) of the same figure, and in the next period of 1/60 sec, the stored mixed signals are read out. As a result, as shown in (C) of the same figure, the odd field signal of n-1 (number) and the even field signal of n are obtained. The odd field signal of n-1 is made up of the mixed signals of line (0+1), line (2+3), line (4+5) . . . which are shown on the left portion of FIG. 17 (B), and the even field signal of n is made up of line (1+2), line (3+4) . . . which are shown on the right portion of FIG. 17(B).
Then, the odd field signal and even field signal are subjected to an interlaced scan to form an image for one frame, and this image is displayed on a monitor. Of course, during the above process, various signal processings are performed to form color difference signals and brightness signals from the above mixed signals, and based on these signals, the image of the inside of a subject to be observed is displayed on the monitor.